2 Warm-up- hand this in for credit 1. Define evolution2. Define natural selection.3. What are the four components that are important in order for natural selection to occur?4. The Hardy-Weinberg equilibrium equation is used to make predictions of allelic and genotypic frequencies for future generations. If a population in a future generation has allelic frequencies that do not match the predicted values, what does this mean?5. You encounter a population in which there are 100 individuals. 25 of these individuals are homozygous dominant.A) what is the allele frequency for this dominant allele?B) What proportion of the next generation’s population should be heterozygous?
3 Evolution Change in allele frequencies in populations over time OR Change in genetic composition in a population from generation to generation (or over time)
4 Natural selectionProcess in which individuals with certain inherited traits tend to survive and reproduce at higher rates than other individuals without those traits
5 Key component of natural selection!! You must know this!! 1. Individuals in a population vary in traits2. These traits must be heritable3. Species can produce more offspring than their environment can support4. Species with certain traits survive and reproduce at higher rates than those without those traits*Individuals do not evolve!! Only populations do!*Natural selection acts on individuals and leads to adaptive evolution!
6 You encounter a population in which there are 100 individuals You encounter a population in which there are 100 individuals. 25 of these individuals are homozygous dominant. A) what is the allele frequency for this dominant allele? B) What proportion of the next generation’s population should be heterozygous?
7 Homework1) Page 491List each type of reproductive barrier, explain it, and give an example. Due tomorrow2) Read pp3) essay #1 due this ThursdayTypo!!!! Recheck the updated version!!!!!
8 The key component for evolution to occur is… Genetic variation!!
9 Genetic VariationGenetic variation among individuals is caused by differences in genes or other DNA segmentsPhenotype is the product of inherited genotype and environmental influencesNatural selection can only act on variation with a genetic component
10 Variation Within a Population Both discrete and quantitative characters contribute to variation within a populationDiscrete characters can be classified on an either-or basisExample: color, shape, presence/absence of a phenotypeQuantitative characters vary along a continuum within a populationExample: body mass, litter sizeDiscrete: colorQuantitative: size
11 Sources of Genetic Variation New genes and alleles can arise by mutation or gene duplicationSexual reproduction produces genetic variation through crossing over, independent assortment, and fertilization
12 Alleles are different variations of a gene Genotypes are combination of alleles that an individual has,One allele came from parent 1, and other came from parent 2
13 Hardy-Weinberg Principle Allele frequencies of alleles and genotypes in a population will remain constant from generation to generation if all assumptions are metA gene pool that remains constant is said to be in Hardy- Weinberg equilibrium
16 Practice on your own : Write this in your notes. What are the genotypic frequencies?What are the allelic frequencies?If there are 700 cats in the next generation, how many of them should be homozygous recessive in the next generation? (assume HW equilibrium)
18 Cystic Fibrosis 1The frequency of cystic fibrosis, a recessive genetic disease, is 1 per 2,500 births among Northern Europeans. Assuming random mating, what is the frequency of carriers?about 0.04%about 2%about 4%The frequency cannot be calculated because selection violates Hardy- Weinberg assumptions.Answer: cThe frequency of carriers is 2pq. The allele frequency, q, is 1/50 since qq = 1/2500. P is close to 1. You may want to discuss why option d does not apply.https://www.polleverywhere.com/multiple_choice_polls/kwbKA0IH4N9iz8I18
19 Cystic Fibrosis 1The frequency of cystic fibrosis, a recessive genetic disease, is 1 per 2,500 births among Northern Europeans. Assuming random mating, what is the frequency of carriers?about 0.04%or about 2%or about 4%The frequency cannot be calculated because selection violates Hardy- Weinberg assumptions.Answer: cThe frequency of carriers is 2pq. The allele frequency, q, is 1/50 since qq = 1/2500. P is close to 1. You may want to discuss why option d does not apply.19
20 Assumptions of Hardy-Weinberg principle Allele frequencies in a population will remain constant if ALL of the following conditions are met:The population is infinitely largeIndividuals mate randomlyNo genetic migrationNo natural selectionNo mutation
21 Three main driving forces that cause changes in allele frequencies Natural selectionGenetic driftGene flow
22 1) Natural selectionProcess in which individuals with certain inherited traits tend to survive and reproduce at higher rates than other individuals without those traitsAdapations are inherited traits that enhance organismal survival and reproduction in specific environmentsFitness: measure of reproductive success associated with a particular trait
23 Natural selection is the only mechanism that consistently causes adaptive evolution Evolution by natural selection involves both chance and “sorting”New genetic variations arise by chanceBeneficial alleles are “sorted” and favored by natural selectionOnly natural selection consistently results in adaptive evolution
24 Types of natural selection DirectionalDisruptiveStabilizing
25 Frequency of individuals Figure 23.13Original populationFrequency ofindividualsPhenotypes (fur color)OriginalpopulationEvolvedpopulationFigure Modes of selection.(a) Directional selection(b) Disruptive selection(c) Stabilizing selection
26 2) Genetic Drift- the reason why large population size is important for Hardy-Weinberg Equilibrium The smaller a sample, the greater the chance of deviation from a predicted resultGenetic drift : when chance events cause allele frequencies to fluctuate unpredictably from one generation to the nextGenetic drift tends to reduce genetic variation through losses of alleles
27 Generation 1 p (frequency of CR) = 0.7 q (frequency of CW) = 0.3 CRCR FigureCRCRCRCRCRCWCWCWCRCRCRCWCRCRCRCWFigure 23.9 Genetic drift.CRCRCRCWGeneration 1p (frequency of CR) = 0.7q (frequency of CW) = 0.3
28 5 plants leave off- spring Figure5plantsleaveoff-springCRCRCRCRCWCWCRCRCRCWCRCWCWCWCRCRCRCRCWCWCRCWCRCWCRCRCRCWCWCWCRCRFigure 23.9 Genetic drift.CRCRCRCWCRCWCRCWGeneration 1Generation 2p (frequency of CR) = 0.7p = 0.5q (frequency of CW) = 0.3q = 0.5
29 5 plants leave off- spring 2 plants leave off- spring Figure5plantsleaveoff-spring2plantsleaveoff-springCRCRCRCRCWCWCRCRCRCRCRCWCRCWCRCRCRCRCWCWCRCRCRCRCWCWCRCRCRCRCRCWCRCWCRCRCRCRCRCRCRCWCWCWCRCRCRCRFigure 23.9 Genetic drift.CRCRCRCWCRCWCRCWCRCRCRCRGeneration 1Generation 2Generation 3p (frequency of CR) = 0.7p = 0.5p = 1.0q (frequency of CW) = 0.3q = 0.5q = 0.0
30 The Founder EffectThe founder effect occurs when a few individuals become isolated from a larger population. Example: wind blows birds off course to another islandAllele frequencies in the small founder population can be different from those in the larger parent population
31 The Bottleneck EffectThe bottleneck effect is a sudden reduction in population size due to a change in the environment , ex: urbanizationThe resulting gene pool may no longer be reflective of the original population’s gene poolIf the population remains small, it may be further affected by genetic drift
32 FigureFigure The bottleneck effect.Originalpopulation
33 Original population Bottlenecking event FigureFigure The bottleneck effect.OriginalpopulationBottleneckingevent
34 Reduction in genetic variation via genetic drift!!! FigureReduction in genetic variation via genetic drift!!!Figure The bottleneck effect.OriginalpopulationBottleneckingeventSurvivingpopulation
35 Case Study: Impact of Genetic Drift on the Greater Prairie Chicken Loss of prairie habitat caused a severe reduction in the population of greater prairie chickens in IllinoisThe surviving birds had low levels of genetic variation, and only 50% of their eggs hatched
36 Greater prairie chicken Figure 23.11Pre-bottleneck(Illinois, 1820)Post-bottleneck(Illinois, 1993)Greater prairie chickenRangeof greaterprairiechicken(a)Numberof allelesper locusPercentageof eggshatchedPopulationsizeLocationIllinois1930–1960s19931,000–25,000<505.23.793<50Figure Genetic drift and loss of genetic variation.Kansas, 1998(no bottleneck)750,0005.899Nebraska, 1998(no bottleneck)75,000–200,0005.896(b)
37 Effects of Genetic Drift: A Summary Genetic drift is significant in small populationsGenetic drift causes allele frequencies to change at randomGenetic drift can lead to a loss of genetic variation within populationsGenetic drift can cause harmful alleles to become fixed
38 3) Gene FlowGene flow consists of the movement of alleles among populationsAlleles can be transferred through the movement of fertile individuals or gametes (for example, pollen)Gene flow tends to reduce variation among populations over timeGene flow can decrease or increase the fitness of a population